FR2472810A1 - BAND THREADER COMPRISING TWO CABESTANS AND CONTROL MEANS FOR CONTROLLING TENSION OF THE TAPE, IN PARTICULAR FOR ELECTROMAGNETIC TRANSDUCERS - Google Patents

Abstract

THE INVENTION CONCERNS TAPE UNWINDERS. ACCORDING TO AN IMPLEMENTATION, THE BAND IS HELD TIGHT ALONG TRANSDUCERS BY TWO CAPSTANS ON EACH OTHER OF THESE TRANSDUCERS. IT IS SUBJECT TO THE ACTION OF THESE TWO CAPSTANS WHICH ARE EACH DRIVEN BY INDEPENDENT MOTOR PLACED UNDER THE CONTROL OF A BAND TENSION CONTROL CIRCUIT, BY APPLYING A HIGHER TORQUE TO THE BAND TAKE-UP CAPSTAN WHICH 'TO THE BAND FLOW CAPSTAN. APPLICATION TO LOW CRYING MAGNETIC TAPE RECORDERS.

Description

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  The present invention relates to tape drives.

  The tape drives are employed with electromagnetic transducers to scroll a magnetic recording tape along a predetermined path passing along said transducers during the recording and reproducing phases of the signals on the tape. In order to guarantee a high fidelity in the reproduction of the signal, several techniques are commonly used. Thus, the movement of

  the band at the level of the transducers is usually produced, directly or indirectly

  directly, by a roller called capstan, which is directly driven by an electric motor. The engine is controlled to rotate this capstan at a stable and precise speed. It is quite desirable that the portion of the strip which is in contact with the transducers is flat, and that is the reason why it is generally subjected to a high tension, for example by means of additional rollers which take up the strip at each of the ends I5 of its path at the level of the transducers, and are placed on the same side of this band to turn it on. However, this technique is not very compatible with a good winding of the band around the receiving coil which requires a low tension of the band. In addition, the presence of additional pebbles

  the free movement of the band and produces vibrations, which is prejudi-

  the smooth passage of the tape over the transducers and translates

  by signal distortions such as wobbling and fluctuation.

  An object of the present invention is to provide a rewinder of

  strips that overcomes these disadvantages.

  According to one aspect of the invention, provision is made

  their tape intended to be used with transducers to scroll

  this band along a predetermined path passing through these transducers.

  characterized in that it comprises: - two capstans, each placed at a respective end of said predetermined path - two rollers each disposed close to one of the two respective capstans and arranged to guide the strip beyond the respective end of said path for partially winding it around the respective capstan, - two drive means, each coupled to one of said respective capstans, and - control means coupled to said drive means and arranged to control rotation of said capstans by different couples to induce

  a controlled voltage in the band along said path.

  Such an arrangement makes it possible to maintain the band under a required high voltage along said predetermined path independently of the

  voltage outside of it.

  Preferably, each of the rollers is mounted to be movable in an arcuate manner around its respective capstan, and is

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  biased in a direction which tends to increase the winding of said band around the capstan. In this case, the rollers themselves can be used to

  control the voltages of flow and recovery of the band (for example in com-

  mandating the movement of the web rolls in connection with the respective roll position along its arcuate stroke), regardless of the tension along

  of said predetermined path at the sensor.

  In addition, the rollers can be selectively movable in directions opposite to those to which they are normally solicited

  in order to reduce the winding arc of said band around the corresponding capstan.

  I0 laying and thus facilitate the loading of the tape in the unwinder.

  A tape drive according to this invention will now be

  holding described by way of example with reference to the accompanying drawings in which:

  FIG. 1 is a diagrammatic plan view of a magnetic tape recorder

  that incorporating the unwinder; Figure 5 is a sectional view along the line II-II of Figure 1; FIG. 3 is a fragmentary plan view of the recorder illustrating the method of placing the strip; and FIG. 4 is a block diagram of part of a servo control circuit

tape drive.

  With reference to FIGS. 1 and 2, a tape recorder generally designated by the reference numeral 10 comprises two reels stores

  strips 12 and 14 which can be used interchangeably to

  biter and receive the tape in the direction of tape scrolling. Each coil 12 and 14 is driven by an electric motor 16 and 18 under the control

a remote control circuit 20.

  As shown in Figure 1, the coil 22 passes from the coil 12 to a first tension roller 24 around which it winds about a half turn. The band 22 is then wound around a little more than half the circumference of a first capstan 26 from which it passes to the level

  four electromagnetic transducers 28 commonly referred to as magnetic heads

  in the direction of a second capstan 30. This capstan 30 and an associated tension roller 32 are symmetrically arranged with respect to the capstan 26 and

  roller 24, and the band 22 wraps around them in the same way before

dye the coil 14.

  Each capstan 26, 30 is arranged to be driven individually.

  by an electric motor, respectively 34, 36, controlled by the servo-control circuit 20. For this purpose, and as shown particularly in Figure 2, the capstan 26 is mounted at the end of a shaft 38 coupled to the motor 34. The lower portion of the shaft 38 supports a transparent tachometric disc 40, having several thousand equidistant radial opacity linear marks interposed between a light source 42 and an optical detector 44. When the disc 40 turns with the capstan 26, the lines regularly cut the light path to the detector 44, the output of which consequently consists of a pulsed signal whose frequency provides an indication of the speed of rotation of the capstan 26. The tachometric signal is sent to the servo-control circuit 20 as a reaction signal to effect the servo-control in a known manner of the power supply of the

  motor 34 and therefore the speed of the capstan 26.

  I0 The tension roller 24 rotatably mounted on an arm 46 freely pivotable on the shaft 38 and which is biased counterclockwise (as shown in FIG. 1) by a tension spring M, fixed the

  arm 46 and a pin 50 mounted on a wheel 52. The wheel 52, which supports one

  The second tenon 54 near the tenon 50 is also mounted to pivot freely around the shaft 38 and is able to be angularly displaced about this shaft 38 by an electric motor 56. A position detector, indicated schematically in FIG. 58 in FIG. 1, provides another reaction signal representative of the position of the arm 46 to the servo control circuit 20 for

  the servo-control in known manner of the drive motor 16 of the coil 12.

  The capstan 30 and the roller 32 are arranged in the same manner as the capstan 26 and the roller 24, and associated with elements comprising a disc, an optical detector 62, an arm 64, a wheel 66, a post 68, an engine 70 and a detector 72 (corresponding to the elements bearing the references 40,44,46, 52,54,56,58 respectively). The capstans 26 and 30 and the tension rollers 24, 32 conventionally have peripheral grooves 74, as shown in FIG. 1, in order to avoid causing air between their respective surfaces and the band at the high speeds thereof. last. The transducers 28 are coupled to the usual conditioning circuitry for recording and reproducing the signal; these circuits are not part of the invention and

  are, therefore, generally indicated at 76.

  In operation, and assuming that the tape secfplace of the

  coil 12 to the coil 14, this band 22 is driven at the level of the trans-

  ducters 28 by the capstans 26 and 30 by the effect of the non-slip contact

  between these capstans and the band. Unlike the systems used earlier

  each capstan 26 and 30 is driven separately by a

  34, 36 and in accordance with the control signals which are sent to it by the servo-control circuit 20, and which are developed in part from the tachometric feedback signals from the detectors 44 and 62. In addition, the servo circuit -commande 20 is arranged to power the motors 34 and 36, so that the capstan "receiver" (in this case, the capstan 30)

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  is driven by a couple a bit higher than is the capstan "debtor" (in this case, the capstan 26). As a result, the capstan 26 tends to rotate slower than the capstan 30 and the portion of the tape passing along the path between the capstans 26 and 30 in front of the transducers 28 is subjected to considerable tension, so as to make this tape good. flat

  and to cause a close and uniform contact between the band 22 and the transducers

  28. If the direction of travel of the web is reversed, the circuit 20 is arranged to drive the capstan 26 (which is now the receiving capstan) to a higher torque than the capstan 30.

I0 (capstan capstan).

  The coils 12 and 14 are driven by their respective motors 16, 18 in response to the control signals from the circuit 20,

  to hold the arms 46 and 64 of the tension rollers in predetermined positions

  determined. These positions, which are identified by the sensors 58 and 72, are selected so as to maintain the web 22 at the desired tension between the spool 12 and the capstan 26, and between the spool 14 and the capstan 30. Frictional contact between the band 22 and the capstans 26 and 30 effectively prevents the high band tension between the capstans 26 and 30 from being propagated along the band beyond these capstans 26 and 30. Tension of the web beyond the capstans 26 and 30 can be separately and independently controlled c the tension of this tape along the transducers 28, and can be adjusted to a different value of the voltage on the path along said

  transducers. In particular, this voltage can be set to a sen-

  lower, suitable for the tape feed, from one of the coils 12 and 14 and more particularly to the recovery of this band of

  uniformly by the other of said coils.

  Thus, the arrangement shown in FIG. 1 makes it possible to reconcile contradictory requirements concerning the tension of the strip

  at different points of its trajectory.

  When it is desired to set up the strip 22 in the unwinder 10, the servo-control circuit can be controlled by a device not shown to-actuate the motors 56 and 70. This causes the wheels 52 and 66 to move from the positions shown in Figure 1 to the positions shown in Figure 3. In particular, the pins 54 and 68 attack the arms 46 and 64 respectively during this operation to push them around the capstans 26 and 30 towards the transducers 28, as shown in FIG. 3. In addition, the transducers 28 may be arranged if desired, to be recessed (for example by cams

  or levers driven by a motor) in relation to their normal position of

  recording or reproduction of the tape. The establishment of the band

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  now only requires the insertion of the band 22 between the capstan 26 and the tension roller 24 and, between the capstan 30 and the tension roller 32, and

  its passage in the vicinity of the transducers 28 along the trajectory represented by

  3. It can be seen that this operation is very simple and does not involve delicate manipulations of the band 22, for example the formation of loops intended to be placed around rollers. Subsequently, the servo-control circuit 20 is actuated to reciprocate the motors 56 and 70 in the opposite direction, which returns the wheels 52 and 66 to the positions shown in FIG. 1, and thus causes the implementation of the IO band 22 along its tortuous trajectory around the capstans 26, 30 and rollers 24, 32. At the same time, the sensors 28 are brought back, if necessary, into

  their normal operating position to come into contact with the band 22.

  It will be understood that the sequence of operations which has just been described may

  for example, to use limit switches for controlling the actuation of the motors 56 and 70, depending on the position of the wheels 52 and 66; the implementation of such details is obvious to those skilled in the art

  and has been omitted from the drawings for the sake of clarity.

  Figure 4 shows the diagram of a possible arrangement

  of the portion of the servo-control circuit 20 which controls the motors of the

bestans 34 and 36. -

  Referring to FIG. 4, the motor 34 receives a supply current from a servo amplifier 100, one of which

  inputs receives a reaction voltage developed by this feed stream.

  at the terminals of a low-value resistor 102 connected in the current path to the motor 34. The other input of the amplifier 100 receives, via a proportional integrator / differentiator 104, the output phase detector 106. This phase detector 106 is powered by the output signal derived from the tachometric disk 40, associated with the motor 34 and with a pulsed signal transmitted to it from a crystal oscillator 108 via of a variable divider 110. The loop 40-106-104-100-34 operates in a manner known per se to drive the motor 34, at a speed which, measured using a tachometric disc 40, is according to the frequency of the pulsed signal, provided by the divider 110. The frequency of this signal depends on

  the frequency of the oscillator 108 (for example, 1.6 MHz) and the division ratio

  N of the divider 11O. A speed control 112 is connected to the divider 110

  to allow different values of N to be selected, and therefore different

rents engine speeds 34.

  The motor 36 is supplied with current in the same way by a servo amplifier 114 associated with a low value resistor 116, a proportional differentiating integrator 118 and a phase detector 12

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  This phase detector 120 receives the engine speed signal derived from the tachometric disk 60, and in normal operation, a pulsed signal from a variable divider 122, which is similar to the divider 110, and the division ratio N

  can similarly be selected by the speed control 112.

  However, unlike the divider 110, the divider 122 is powered by a pulsed signal from a voltage controlled oscillator

  (VCO) 124 which operates in response to a control voltage transmitted to it

  put through a control loop filter 126 by a comparator 128. An input of this comparator 128 is connected to receive a reference voltage from a variable resistor 130, while the other input receives, through a switch 131, an output signal of a differential amplifier 132, the inputs of which are connected to receive the voltages of

  reaction developed across the resistors 102 and 116.

  The functional characteristics inherent to the I5 printed circuit motors 34 and 36 are such that the torques they develop are proportional to the current currents flowing through them. Thus, the reaction voltages across the resistors 102 and 116 are indicative of the torques.

  developed by the respective motors 34 and 36, and the output signal of the

  differential plifier 132 is indicative of the difference between these couples

  (i.e., the difference in the torques applied to capstans 26 and 30).

  The VCO 124 is controlled by the comparator 128 to provide a pulsed signal to the phase detector 120 via the divider 122, so that the output signal of the differential amplifier 132 remains equal to the reference voltage preset by Adjusting the adjustable resistor 130. Therefore, the motor 36 is actually powered to develop a torque that differs from that developed by the motor 34 by an amount that depends on the magnitude of the predetermined reference voltage (and which can be controlled by setting the latter). If the running direction of the web is reversed, the switch 131 is changed in position relative to that shown for

  interpose an inverter 133 between the differential amplifier 132 and the comparator

  controller 128 so as to thereby reverse the input signals of the amplifier

  132 necessary to maintain equilibrium at the comparator 128.

  In practice, the actual frequency of the VCO output signal

  124 will not differ much from that of Oscillator 108. The difference in torque

  results from phase differences between the two signals. Any difference

  This frequency is representative of a malfunction, such as the loss of its locking position by the VCO 124 which must be detected and corrected in order to avoid damaging the tape 22 and / or the tape drive.

  For this reason, the reaction signals from the tacho

  meters 40 and 60 are also transmitted to a frequency comparator 134.

  Y 7- This provides a signal representative of the frequency difference at an input of a comparator 136, whose other input receives a reference voltage from an adjustable resistor 138. The output of the comparator 136 controls the coil of a relay 140 associated with a bi-polar switch 142 interposed between the variable divider 122 and the phase detector 120. This bi-polar switch

  is normally in the position shown in Figure 4, connecting the detection

  phase 120 to receive the output signal of the divider 122. However, in the case where the frequency difference between the feedback signals from

  divisors 110 and 122 exceed a limit corresponding to the reference voltage.

  I0 rency established by setting the resistor 138, the comparator 136 actuates the coil of the relay 140. The switch 142 is then reversed to connect the phase detector 120 to receive the same signal as the phase detector 106, from the divider 110. This causes the two control loops to be powered by the same reference signal, thereby enabling VC0 124

  I5 to restore this frequency lock.

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Claims (6)

  1. A tape dispenser for use with transducers to scroll this band along a predetermined path passing at the level of said transducers characterized in that it comprises - two capstans (26,30) each disposed at a respective end of said predetermined path   - two rollers (24,32), each arranged in the vicinity of one of the said   respective bestans (26,30) and arranged to provide partial winding of the strip 22 beyond the respective end of said path around the respective capstan (26,30);   Io - two drive means (34,36) each coupled to one of said cabs-   tans (26,30) respectively; and - control means (20) coupled to said drive means (34,36) and arranged to control the rotation of said capstans (26,30) under the action of different torques to induce controlled voltage in the band I5 along said path.   The belt weeder according to claim 1, characterized in that each of said rollers (24, 32) is mounted so as to be movable along an arcuate path around the corresponding capstan (26, 30). and is biased in a direction that tends to increase the winding angle   said band (22) around this capstan.   Belt unwinder according to Claim 2, characterized in that the rollers (24, 32) also serve for controlling the supply voltage. and tape recovery.   4. Belt unwinder according to one of the preceding claims,   characterized in that the rollers (24,32) are selectively movable in   opposite directions to those in which they are normally   to reduce said winding angle of the strip (22) and to facilitate   loading this tape (22) into said unwinder.   The tape dispenser according to any one of the preceding claims   in which said control means comprise a servo-control loop in which is included one of said drive means,   and which is coupled to a first source of oscillation signals for controlling   der in response thereto said drive means as a function of the frequency of these oscillation signals, and characterized in that said control means (20) comprise a second servo-control loop (36,, II4, II8, I20) in which the other drive means (36) is included and coupled to a second oscillation signal source (I22, I24) for controlling said further drive means (36) in accordance with the frequency of said oscillation signals, and in that said second oscillation signal source (I22, I24) is coupled to sensitive means (I28, I30, I32).   to the couples developed by said drive means (34,36).   I0 6. Belt unwinder according to claim 5, characterized in that it further comprises frequency comparison means (I34, I36) responsive to the difference between the speeds of said capstans (26,30) and to couple said second loop servo-control (36, 60, II4, II8, I20) to said first source (I08, IIO) if said difference in speed exceeds a predetermined threshold.